@article{MAN_1989__285_1_164604,
     author = {Francois Lalonde},
     title = {Classes caract\'eristiques isotropes.},
     journal = {Mathematische Annalen},
     pages = {343--352},
     publisher = {mathdoc},
     volume = {285},
     number = {1},
     year = {1989},
     zbl = {0662.55009},
     url = {http://geodesic.mathdoc.fr/item/MAN_1989__285_1_164604/}
}